Frederick Courteney Selous - African Nature Notes and Reminiscences

Published by Good Press, 2019

EAN 4057664606648

Table of Contents

Table of Contents

NOTES ON THE QUESTIONS OF PROTECTIVE COLORATION, RECOGNITION MARKS, AND THE INFLUENCE OF ENVIRONMENT ON LIVING ORGANISMS

Harmony of colour in natureTheory of protective colorationSexual selectionConspicuous colours not harmfulThe influence of environmentThe leucoryxThe Barbary sheepThe Sardinian moufflonAfrican butterfliesColoration of the musk ox and caribouArctic hares and foxesColoration of mammals in the Yukon TerritoryThe chamois in winterExamples of conspicuous coloration in African mammalsColour not always protectiveCarnivorous animals usually hunt by scentWild dogs and wolvesWild dog and sable antelopeSense of smell in herbivorous animalsSight of antelopesExperience with waterbuckDull sight of caribouDemeanour of wild animals when alarmedSmall antelopesLionsLarge antelopesDifficulty of seeing wild animals sometimes exaggeratedPowers of sight of BushmenColour not protective against animals which hunt by night and by scentAnimals in motion easy to seeRestlessness of wild animalsLions attacking bullocksZebras the principal prey of lions since the disappearance of buffaloesAppearance of zebrasUndoubtedly conspicuous animals in open countryZebras by moonlightStrong smell of zebrasConspicuous antelopes in East AfricaEffect of the juxtaposition of black and whiteBold coloration of the sable antelope.

Although there are certain striking exceptions to the general rule, yet, broadly speaking, it cannot be gainsaid that living organisms are usually coloured in such a way as to make them difficult of detection by the human eye amongst their natural surroundings. Every collecting entomologist knows how closely certain species of butterflies when resting with closed wings in shady forests resemble dead leaves, or moths the bark of trees. Birds too, especially those which nest on the ground, often harmonise with their surroundings in a most marvellous way.

In the open treeless regions within the Arctic Circle, as well as on bare mountain ranges, nearly all the resident species of animals and birds turn white in winter, when their whole visible world is covered with an unbroken mantle of pure white snow, and become brown or grey during the short period of summer.

In treeless deserts again within the tropics, where the rainfall is very scanty and the climate excessively hot and dry, with intense sunlight throughout the year, all resident living organisms, mammals, birds, reptiles, and insects, are found to be of a dull coloration which harmonises in the most wonderful way with the sandy or stony soil on which they live. It is also very often the case that animals which live in forests where the foliage is not too dense to allow the sun to penetrate are spotted or striped, whilst those which live in really thick jungle or amongst deep gloomy ravines are of a uniform dark coloration.

Now a most interesting question arises as to the true causes which have brought about the extraordinary variations of colour to be seen in living organisms inhabiting different parts of the world.

It is, I believe, the general opinion of modern naturalists that, putting aside cases where brilliant colours may have been produced amongst birds and insects by the action of the law of sexual selection, the coloration of all living organisms is protective, "serving," as that distinguished naturalist Mr. Alfred Russel Wallace puts it, when discussing the subject of the coloration of mammals, "to conceal herbivorous species from their enemies, and enabling carnivorous animals to approach their prey unperceived."

Many very striking facts can be adduced in support of this theory, and no doubt it is of advantage to most species of mammals, birds, reptiles, and insects to harmonise in colour with their surroundings; but there are many instances in nature, especially amongst birds and insects, where a very striking and conspicuous coloration does not appear to have been prejudicial to the life of a species.

The highly decorative but very conspicuously coloured plumage to be seen in the males of many species of birds, especially during the breeding season, was considered by the immortal Darwin to be due to the influence of sexual selection, and whatever may be urged against the correctness of this theory, it is supported by a long array of indisputable facts.

Great, however, as is the divergence between the plumage of the males and females in many species of birds, not only during the breeding season, but in a great number of cases at all times of year, and however gaudy and conspicuous the coloration of the former may be compared with that of the latter, such conspicuous coloration never appears to be prejudicial to the life of a species, though in some cases the brighter coloured male assists the female in incubation, and it would thus appear that in all such cases the sombre coloured plumage of the female was not absolutely necessary for purposes of protection against enemies.

I therefore think that if it is admitted that bright and conspicuous colours have been evolved in living organisms through the action of the law of sexual selection, without detriment to the life of the species in which such conspicuous colours are shown, it must be conceded that a coloration harmonising with its surroundings is not a necessity of existence in all cases to all species of mammals, birds, reptiles, and insects, and that it is therefore quite possible that where living organisms agree very closely in colour with their surroundings, such harmonious coloration may have been produced by some other agency than the need for protection by colour, and I would suggest that in addition to the influence exerted in the evolution of colour in living organisms by the action of sexual selection, and the necessity for protection against enemies, a third factor has also been at work, which I will call the influence of environment.